A current sensor has been proposed that detects a current based on characteristics of a Hall element, which is a semiconductor element. When a control current flows through the Hall element and a magnetic field is applied to the Hall element in a direction perpendicular to the control current flow direction, a Hall effect occurs and a Hall voltage is induced across the Hall element.
When a current to be detected flows through a conductor, the magnetic field is generated around the conductor in a direction perpendicular to the detected current flow direction. The magnetic field changes proportional to the amount of the detected current. Therefore, the detected current can be measured by the Hall element placed near the conductor. Specifically, the detected current can be measured based on the Hall voltage generated by the Hall element that is placed near the conductor such that the control current flow direction is parallel to the detected current flow direction.
Typically, the Hall element and peripheral circuits are integrated into a Hall IC. The use of the Hall IC reduces the size and manufacturing cost of the current sensor.
In the current sensor using the Hall IC, a portion of the magnetic flux induced around the conductor by the current leaks so that the whole magnetic field is not applied to the Hall IC. As a result, the current sensor may not accurately detect the current.
To overcome the above problem, a current sensor with a magnetic core has been proposed and used in practice. The magnetic core is made of a magnetic material such as permalloy and concentrates the magnetic flux. For example, in a current sensor disclosed in JP-2002-148284A, the magnetic core is installed in a case by insert molding technology and then a circuit board having the Hall IC is placed in the case.
In such a current sensor having the magnetic core, the positional relationship between the magnetic core and the Hall IC affects the strength of the magnetic field around the Hall element. Therefore, the current sensor requires high assembly precision. Even if the requirement for the high assembly precision is met, the positional relationship may change over time due to, for example, change in the ambient temperature. As a result, the current sensor may not accurately detect the current.
The current sensor needs to detect a small current, i.e., needs high sensitively, because recent development trends are toward low power consumption. In the current sensor, the Hall IC is placed in a gap of the magnetic core and the magnetic flux flowing through the magnetic core is applied to the Hall element of the Hall IC. The sensitivity of the current sensor can be increased by reducing a gap separation distance in order to increase the magnitude of the magnetic flux applied to the Hall IC.
However, since the Hall element is integrated in the Hall IC, the gap separation distance may be limited to the thickness of the Hall IC. Further, when the Hall IC is placed in the gap with the reduced separation distance, the assembly precision may need to be further improved.